Why is it always like this?

I bet that all of you have felt like this at least once. What I'm mumbling about here? The matter of fact that all of us felt that we don't belong in this place. For one it's a thought of a minute, for another a thought of a day, for some a thought of a week, for other a thought of a month and for the rest of us...a thought of a lifetime. We feel incomplete, empty, unwanted, unloved...but still, we continue to live.
Maybe you have felt like you aren't doing anything with your life. You see all these people on Tv or read about someone doing something extraordinary and here you are: listening to your parents, learning things you may not need ever in your life just to have a "future". And there are people your age whose lifes are perfect! They are independent, free, have money on their own, are beautiful...seems like life loves them quite a lot, doesn't it? And you start to feel useless and think of ways to become like them...But it's rather foolish, isn't it?